The present disclosure is related to a patient support apparatus having frame and deck members that move relative to one another. More specifically, the present disclosure is related to a patient support apparatus having sensors which detect when frame and deck members encounter obstructions and a control system that modifies movement of the patient support apparatus based on the information from the sensors.
Patient support apparatuses such as hospital beds, for example, may include frames that move relative to one another, and deck sections that move relative to a frame. The patient support apparatus may include a lower frame, also known as a base frame, and an upper frame which moves relative to the lower frame. The upper frame may be supported on various structures which cause the upper frame to move relative to the lower frame. In some cases, the upper frame is supported on two hydraulic cylinders and is movable relative to the lower frame when the hydraulic cylinders are extended and retracted. In some cases, the upper frame is supported on one or more lift arms that are driven by hydraulic cylinders or motorized actuators. Movement of the lift arms causes the upper frame to move relative to the lower frame. If one of the drives or hydraulic cylinders is driven at a different rate as compared to the other of the drive or hydraulic cylinders, the upper frame may move to a tilt position as compared to the lower frame.
Patient support deck sections are supported on an upper frame and pivotable relative to the upper frame to raise or lower portions of a patient's body. For example, a head deck section may rise relative to the upper frame to incline the patient's torso. In some cases, a thigh deck section that supports a portion of the patient's seat and thighs may also pivot relative to the upper frame. In some cases, a foot deck section may be pivotable relative to a thigh deck section to change the angle between the thigh deck section and the foot deck section. It is also known to have a foot deck section that is extendable and retractable to change the length of the foot deck section.
In some patient support apparatuses such as the Hill-Rom® TotaleCare® bed, for example, the bed is capable of being moved to a position in which a patient may exit, or egress, from the foot end of the bed when the bed has been moved to a chair configuration. This position is generally known as a “chair egress position.” In the chair egress position, the upper frame may be tilted relative to the lower frame, the foot deck section may be pivoted relative to the thigh deck section, and the head deck sections may be pivoted relative to the upper frame. The positions of the various frames and deck sections are monitored by position sensors that provide feedback to a controller to confirm that the frame members and the deck sections are in positions that will not result in contact between frame members and deck section members or between the frame members and deck section members and the floor.
In some cases, potentiometers are connected between two members that move relative to one another. The potentiometers are used to determine the relative movement between the members. For example, a potentiometer may be positioned between a left arm and a lower frame member to determine the amount of movement of the left arm relative to the lower frame. In some cases, a potentiometer is used to measure the length of a hydraulic cylinder or motorized actuator. The amount of movement of the lift arm relative to lower frame, or the length of the cylinder or motorized actuator, are used to determine a relative position of two members of the patient support apparatus. It is also known to use accelerometers to determine the attitude of a frame number or deck section member with the controller utilizing the attitude of the various deck section members and frame members to determine the orientation of the various members relative to one another.
The use of sensors to determine the relative position of frame members and deck section members requires a designer to utilize the kinematic relationship of the various frame members and deck section members to develop logic in the controller to prevent movement to of frame members or deck section members to unacceptable positions. Such relationships are subject to variations in manufacturing tolerances and the accuracy of the sensors used to measure the relationships. These limitations sometimes cause designers of the patient support apparatuses to limit the range of movement of frame members and deck section members to be sure that any movement is outside of any variation which may be expected from sensor limitations or manufacturing variations.